Dielectric material and process of making the same



Oct. 19, 1937. J, w JIRA 2,096,550

DIELECTRIC MATERIAL AND PROCESS OF MAKING THE SAME Filed March 28, 1936 INVENTOR.

Jose il W Jira. ,5 w

ATTORNEY.

Patented on. 19, 1937 PATENT OFFICE DIELECTRIC MATERIAL AND PROCESS OF MAKING THE SAME Joseph William Jira', Newburgh Heights, Ohio, assignor to Continental Carbon Inc., Cleveland, Ohio, a corporation of Ohio Application March 28, 1936, Serial No. 71,521

Claims.

My invention relates to dielectric materials the process of making the same.

An object of my invention is to provide a dielectric medium having a high dielectric constant and a low power factor.

Another object of my invention is to provide a dielectric medium having a substantially stable and dielectric constant and a substantially stablev power factor throughout a relatively wide range of temperatures.

A further object of my invention is to provide a dielectric medium having a dielectric constant which slightly increases with decreasing temperature, even for decreasing temperatures ber low 20 degrees centigrade.

It is also an object of my invention to provide a dielectric medium having a low viscosity and a low effective conductivity, thereby producing a medium having a low ionic density or a low 17M factor.

A still further object of my invention is to provide a dielectric medium which has a low,

moisture absorption co-efiicierit, and which is not subject to deterioration by oxidationwhen exfied by a radical of the group consisting of alkyl radicals, or by a radical of the group consisting of aryl radicals, or by a combination of the two.

Other objects and a better understanding may be had by referring to the following description and claims, taken in combination with the accompanying drawing, in which:

The figure illustrates two curves, one of which shows the dielectric medium embodying the features of my invention, throughout a range composed of various proportions of chlorodiphenyl, diamyl phthalate, and a mineral oil.

The conductivity of liquid dielectrics is ionic in character, and the value of the conductivity depends on the number of ions present and on their mobilities or specific velocities. For ions of a given size the mobilities are in general, in-

versely proportional to the viscosity. Thus,- a certain relationship exists between various liquid dielectrics; in that, they vary in viscosity, which may be indicated as 1 being measured in poises, and in conductivity, which may be referred to 5 as M being measured in mho per cm. with temperature. For convenience, instead of using the term conductivity, the term effective conductivity may be used, since the loss is wholly due to conduction. Since the effective conductivity is directly proportional to the number of ions present and inversely proportional to the viscosity, the factors 1m are an indication of the number of free ions present. We have then in this factor, a property of the liquid dielectric which is independent of the temperature. Varioustypes of liquid dielectrics, therefore,.differ markedly as related to the value of this factor. Obviously, it is not to be expected that the value of 1m should remain constant over any very great range of temperatures. In the lower range, as the liquid dielectrics tend to stiffen, it is probable that the inverse relationship between mobility and viscosity does not hold. In the upper temperature range, it is probable that further 25 new ions are generated. Therefore, the number of free ions present is to some extent a measure of the purity of the oil.

In a search to obtain a good dielectric possessing a' low ionic density or a low 1 x0 factor, many synthetic resins have been investigated, especially those centered about the halogenated cyclic hydrocarbon compound, or mixtures of halogenated cyclic hydrocarbon compounds. Of these halogenated cyclic hydrocarbon compounds, the group characterized generally as the chlorinated diphenyl compounds appear to possess the best properties for a good dielectric medium. The chlorinated diphenyl group was found to possess a high volume resistivity or insulating property, as well as an excellent water resisting quality or a low moisture absorption coefllcient. This prevents the presence of water which is detrimental to a good dielectric.

It was especially noted with reference to the chlorinated diphenyl group that the dielectric constant and the power factor varied with the degree of chlorination of the diphenyl. By reason of this variable relationship, theelectrical characteristics of the dielectric medium may be controlled to give the desired operating performance for each specific electrical device in which the dielectric medium is used by varying the degree of chlorination of the diphenyl. For example, starting with approximately 10% chlorination, the dielectric constant of the dielectric medium is of a low value, but gradually increases in value until it reaches a maximum value in the neighborhood of 40% chlorination of the diphenyl. Beyond this maximum Value, the dielectric constant gradually decreases until it reaches a second low value in the neighborhood of 60% chlorination or higher. The power factor of the chlorinated diphenyl also has an ascending and descending characteristic very much like the general outline of the'characteristic for the dielectric constant. For example, starting with a relatively low percentage of chlorination, the power factor is relatively low,

- solid structure.

but gradually increases to a maximum value in -the neighborhood of 30% chlorination. Beyond this maximum value, the power factor gradually decreases to a low minimum at about 54% chlorination, beyond which point the power factor gradually increases, as the percentage of chlorination is increased' Physically, chlorinated diphenyl is a liquid of low viscosity at the early stages of chlorination, but gradually increases in viscosity with a rise in the percentage of chlorination up to approximately 60% chlorine, beyond which point a solid is produced, and is characterized by its clear.yellow to opaque Aside from the fact that the chlorinated diphenyl has a relatively high power factor and a relatively low dielectric constant at high stages of chlorination, it is not suitable, in

itself, for the manufacture of electrostatic capacitors, by reason of the difficulties encountered in impregnation.

While the 7m factor, and the dielectric constant and the power factor of the liquid chlorinated diphenyl compounds, as well as the various aryl asv well as the various aryl isomeric mixtures, is.

very detrimental to. the successful operation of capacitors, especially where the capacitors are used for power factor correction, particularly in outside installations where the temperature may be low in the winter months.

I have discovered that this objection of instability of the dielectric constant and the power factor may be overcome by using the halogenated cyclic hydrocarbon compounds, and particularly the chlorinated diphenyl compounds, as well as the various aryl isomeric mixtures thereof with high boiling esters, known as phthalates, These phthalates may be produced by the interaction of phthalic anhydride or acid with either aliphatic or aromatic alcohols or their isomers or the combination of the aliphatic or aromatic alcohols. In other words, the phthalate compound may comprise any one of three principal chemical structures. 'First, the phthalate compound may comprise an ester of phthalic acid having both of the carboxyl groups satisfied by a radical of the group consisting of alkyl radicals, such for exam ple, as alcohols of the, methane series. Second,

the phthalate compound may comprise an ester aoaasso of phthalic acid having both the carboxyl groups satisfied by a radical of the group consisting of aryl radicals, such for example, as alcohols of the benzene series. Third, the phthalate compound may comprise an ester of phthalic acid having one of the carboxyl groups satisfied by a. radical of the group consisting of alkyl radicals, such for example, as alcohols of the methane series, and having the other carboxyl group satisfied by a radical of the group consisting of aryl radicals such for example, as alcohols of the benzene series. Also there is a fourth possibility of using a phenol compound in place of an alcohol in the formation of phenolic ester. A type of this kind of ester is phenyl ester.

The combination of the halogenated cyclic hydrocarbon compounds and the phthalate compounds, as above described, is particularly adapted for electro-static capacitors, for the reason that the electrical characteristics of the said medium may be controlled by the type of phthalate incorporated within the halogenated cyclic hydrocarbon compounds. Thus, the phthalate compound produced by the combination of phthalic anhydride and the alcohol of the methane series gives a different electrical characteristic from the phthalate compound produced by the combination of a phthalate anhydride and an alcohol of the benzene series. 'Also, the phthalic combinations produced by the different alcohols of the methane series themselves are slightly different from each other in electrical characteristics. Thus, the diethyl and dimethyl phthalates produce a higher specific inductive capacity or dielectric constant than the dibutyl and the diamyl phthalates, but the former are accompanied with a higher power factor and a lower volume resistivity.

For example, I have found that a mixture composed of 70% by weight of diamyl phthalate and 30% by weight of 65% chlorinated diphenyl, which is a resinous solid, produced a liquid dielectric of very low viscosity and a low eifective conductivity, giving rise to a very low 1 x factor. The power factor in the above mixture was less than .001 and the dielectric constant was approximately 6.3. A second mixture composed of 40% diamyl phthalate and'50% of 65% chlorinated diphenyl and 10% heavy liquid petrolatum, all measurements by weight produced a very mobile liquid having a relatively high dielectric constant and a very low power factor. The power factor in this case was approximately .0005 and the dielectric constant was 5. Of course, these examples represent only in a general manner what changes were found to exist in the electrical characteristics of the dielectric medium by varying the phthalate incorporated therein.

In the figure, I show two electrical characteristic curves, one of which is the dielectric constant curve, and the other is the power factor curve for a dielectric medium composed of various proportions of chlorinated diphenyl, diamyl phthalate, and mineral oil. As illustrated, the dielectric constant and the power factor is measured as ordinates and the various proportions of chlorinated diphenyl, diamyl phthalate, and mineral oil are measured as the abscissa. At the left end of the abscissa, the ratio is 10:0:0; meaning that the mixture comprises 10 parts of chlorodiphenyl, zero parts of diamyl phthalate, and zero parts of mineral oil. On the extreme right end of the abscissa, the ratio is 0:10:0; indicating that the mixture comprises zero part of chlorodiphenyl, 10 parts of diamyl phthalate, and zero parts of mineral oil. As the ratio proceeds from the left to the right along the abscissa, the chlorodiphenyl content gradually decreases and the diamyl phthalate gradually increases. This gives a variable ratio of chlorodiphenyl to diamyl phthalate. The mineral oil content is maintained at a constant value of 1 part,

. throughout the entire range, except for the two proaches the right hand side of the abscissa.

.The power factor characteristic takes the shapesubstantiallyof a catenary. Beginning at the left with a ratio of 10 parts of chlorodiphenyl, zero parts of diamyl phthalate, and zero parts of mineral oil, the power factor is substantially 4%, but has a drooping characteristic like a catenary as the ratio proceeds to the right along the abscissa to a point substantially midway between the two extremes, at which point the curve begins to rise gradually, which finally terminates with a relatively high power factor of substantially .8% at the right hand end of the abscissa where the ratio of the mixture is zero parts of chlorodiphenyl, 10 parts of diamyl phthalate, and zero parts of mineral oil. As illustrated by the curve, the power factor is less than .1 per cent beginning with a ratio 7:2:1 and extending over to the ratio 2:7:1. In other words, the range of the ratio of chlorodiphenyl to diamyl phthalate varies from substantially .3 up to 3.5, reading from right to left. These curves in the figure were produced under the temperature condition of approximately 20 ,degrees C. Also, the chlorodiphenyl had,a chlorination percentage in the neighborhood of 65, giving what is known as the Heptachlor series, characterized by their clear yellow to opaque solid structure. Thus, we observe from thecurve that the power factor of the chlorodiphenyl itself, that is, without the diamyl phthalate and the mineral oil is relatively high and the dielectric constant is relatively low. However, upon treating the chlorinated diphenyl with diamyl phthalate, and mineral oil, the dielectric constant was increased to a value higher than 6, and the power factor was reduced to a value as low as .0005, which gives a very good electrical characteristic. Furthermore, the mixture of the chlorinated diphenyl and the diamyl phthalate was such that the dielectric constant a and the power factor was stable throughout a 'it with the halogenated cyclic hydrocarbon compound.

Instead of using the chlorinated diphenyl, I find that such synthetic waxes such as the group of chloronaphthelenes, may be used with the phthalate compounds. Physically, the groups of chloronaphthelenes are solids of crystalline structure possessing high densities. Electrically, the

chloronaphthelenes possess a fairly high dielectric constant and a volume resistivity as well as a fairly low power factor.-

Although I have described my invention with a certain degree of particularity,'it is understood that the present disclosure has been made only by way of example and that numerous changes in the details of the combination and arrangement of substances may be resorted to without departing from the spirit and scope of the invention as hereinafter claimed.

I claim as my invention:

1. A dielectric medium comprising as substantial ingredients the combination of a halogenated cyclic hydrocarbon compound, and an ester of phthalic acid having the carboxyl groups satisfled by a radical of the group consisting of alkyl and aryl radicals.

2. A dielectric medium comprising as substantial ingredients the combination of a halogenated cyclic hydrocarboncompound, and an ester of phthalic acid having the carboxyl groups satisfied by a radical of the group consisting of alkyl radicals.

3. A dielectric medium comprising as substantial ingredients the combination of a halogenated cyclic hydrocarbon compound, and an ester of phthalic acid having the carboxyl groups satisfied by a radical of the group consisting of aryl radicals.

4. A dielectric medium comprising as substantial ingredients the combination of a halogenated cyclic hydrocarbon compound, an ester of phthalic acid having one carboxyl group satisfied by a radical of the group consisting of alkyl radicals and the other carboxyl group satisfied by a radical of the group consisting of aryl radicals.

5. A dielectric medium comprising as substantial ingredients the combination of a halogenated cyclic hydrocarbon compound, and a diamyl phthalate.

6. A dielectric medium comprising as substantial ingredients the combination of a halogenated cyclic hydrocarbon compound, and an amyl phthalate.

7. A dielectric medium comprising as substantial ingredients the combination of a halogenated cyclic hydrocarbon compound, and a dibutyl phthalate.

8. A dielectric medium comprising as substantial ingredients the combination of a chlorinated diphenyl, and a diamyl phthalate.

9. A dielectric medium comprising as substantial ingredients the combination of a chlorinated diphenyl, and a diamyl phthalate, the ratio of the chlorinated diphenyl and the diamyl phthalate varying from .3 to 3.5.

10. A dielectric medium comprising as substaningredients the combination of a chlorinated diphenyl, and a diamyl phthalate having a dielectric constant greater than 4 and a power factor less than .001 in the neighborhood of-20 degrees C.

11. A dielectric medium comprising as substantial ingredients the combination of a chlorinated diphenyl, and a diamyl phthalate having a substantially catenary power factor characteristic throughout the range of ingredients defined at one limit by a large proportion of chlorinated diphenyl and a small proportion of diamyl tial ingredients the combination of a chlorinated naphthalene, and a diamyl phthalatc.

13. A dielectric medium comprising as substantial ingredients the combination of chlorinated diphenyl, a diamyl phthalate, and a mineral oil.

14. A dielectric medium comprising as substantial ingredients the combination of a halo-- aocacso 17. A dielectric medium comprising as substantial ingredients the combination of chlorinated diphenyl consisting of over 60 per cent chlorine, and

an ester of phthalic acid having the carboxyl groups satisfied by hydrocarbon radicals.

18. A dielectric medium comprising as substantial ingredients the combination of a halogenated cyclic hydrocarbon compound, and an ester of phthalic acid having one of the carbonyl groups satisfied by a hydrocarbon radical.

19. A dielectric medium comprising as substantial ingredients the combination of a halogenated cylic hydrocarbon compound, and an ester of phthalic acid having the carbonyl groups satisfied by hydrocarbon radicals.

20. A dielectric medium comprising as substantial ingredients the combination oi a halogenated cyclic hydrocarbon compound, and an ester of u phthalic acid in which the hydrogen of the carboxyl groups in the phthalic acid are substituted by a hydrocarbon radical.

JOSWH JIRA. 

